1. Technical Field
The present invention relates to a technique for measuring a three-dimensional shape of a surface of a measurement target object.
2. Related Art
A technique is known in which an image captured by a camera is analyzed to obtain a normal line (or gradient) on a surface of a measurement target object, thereby restoring the three-dimensional shape of the surface. For example, Patent Document 1 discloses a method for measuring the gradient of a solder surface by emitting a concentric pattern of light from ring illuminators disposed in multiple stages. Also, Patent Document 2 discloses a method for restoring the shape of the surface of a body tissue by irradiating a light pattern onto the body tissue with a medical endoscope, and calculating a normal line based on the specular direction of the light. Also, Patent Document 3 discloses a method for measuring the gradient of a solder surface after the reflow process by using parallel light illumination and a line sensor. Other than those, methods are known such as a method in which a normal line on the surface of an object is obtained by sequentially turning on a plurality of light sources and observing changes in shadows in the object (so-called a photometric stereo method), a method in which the orientation of a normal line to the surface of an object is obtained by irradiating the object surface with three colors of light, namely, red light, blue light and green light, at different angles, and observing the color of the object surface (structured-light method).